(1) Field of the Invention
The present invention relates to a color signal generating device for a display device for displaying color images.
(2) Related Art Statement
A great number of display devices for reproducing images have been proposed and used. The properties of such display devices are evaluated on the basis of their characteristics, such as the resolution, the brightness, the contrast, and the color reproducibility, and compared. In some cases, different weight is given to these values for determination, depending on the environment in which the display device is used.
In the case where a display device, for example a portable terminal, is carried around and used in various environments, the surrounding brightness (luminous intensity) changes greatly. It is desired for the brightness of the screen to be high, in order to maintain the visibility of the screen even in bright places. As a method for forming a display device for increasing the brightness, there is a method for adding W pixels. In general, the pixels of a display device are formed as a combination of three colors: R, G and B (red, green and blue).
In the comparison using the wavelength distribution, R, G and B have only a partial wavelength range, while W has a broader wavelength range covering R, G and B. In other words, W is an achromatic color having no significant wavelength distribution. Therefore, W is appropriate for achieving higher brightness than R, G and B. Thus, the above described object of increasing the brightness can be achieved by adding W as pixels for the display device.
Many signal systems for expressing images using analog or digital signals have been proposed in order to reproduce images using a display device. There are RGB, CMY, YUV and XYZ, for example as signal expressions for color based on the human sense of sight. It is known that the resolution in terms of the brightness is higher than the resolution in terms of colors to the human sense of sight. Television broadcasting signals are an example of a signal format based on this fact, and a technology using the brightness Y and a color difference signal C as color signals and setting the frequency properties of the former higher than the latter is used.
Incidentally, the configuration of pixels for inputted color signals is not created on the basis of the pixels in the display device as in the above described example of television signals. Accordingly, signal conversion in the configuration of the pixels becomes indispensable in the generation of drive signals for a display device using RGBW as described above when general color signals are inputted.
Patent Document 1 relates to such signal conversion.
(Patent Document 1) Japanese Translation of International Unexamined Patent Publication 2004-538523